The present invention relates to a photoimaging and thermal development recording media utilizing microcapsules.
Examples of a photoimaging recording media utilizing microcapsules include U.S. Pat. Nos. 4,529,681 (Usami et al.), 4,916,042 (Sakojiri et al.), 4,440,846 (Sanders et al.), 4,339,209 (Sanders et al.), and U.S. patent application Ser. No. 407,406 (Sakojiri et al.) filed on Sep. 14, 1989.
Those recording media utilize photoimaging forming materials such as a polymerizable monomer, photopolymerization initiator, and/or dye precursor etc. contained in the microcapsules as the main compounds. When a recording sheet (such as a plastic film) is coated with the microcapsules and image-wise exposed with light, the exposed portion of the microcapsules harden. Pressure or heat is applied to the unexposed portion of the microcapsules to emit the compounds contained in the microcapsules to form an image.
However, the conventional photopolymerization initiator is mainly a water soluble pigment and suffers from serious drawbacks. The water soluble pigment is easily diffused into a water phase which causes difficult emulsification while the microcapsules are produced. Consequently, the obtained microcapsules are not evenly photosensitized. At the worst, some conventionally produced microcapsules remain unhardened even if exposed.
In particular, monomer polymerization requiring light energy does not produce a sufficiently strong polymer because the photopolymerization initiator is inactivated by water. The grown-polymer-radical and water react with each other, and the polymerization reaction is stopped and a polymer of a low molecular weight is produced. If this sort of polymerizable monomer is contained in the microcapsules, the contained water in the polymerizable monomer increases during the process of microencapsulation. This contained water impedes the photopolymerization reaction, and the exposure of the light energy does not enable a sufficient hardening of the microcapsules thus lowering the microcapsule photosensitivity.
Further, a nonionic surfactant such as polyvinyl alcohol (PVA), polyethyleneglycol (PEG), and sorbitan derivative are conventionally used as the surfactant for producing the microcapsules.
The microcapsules including the polymerizable monomer are compounded with the nonionic surfactant, however, polymerization reaction, such as radial polymerization, is impeded by the invasion of water in the microcapsules through the process of microcapsulation. Accordingly, the conventional microcapsule polymerization process still results in low-weight molecules, or the polymerization process does not produce any reaction at all, and thus the internal part of the microcapsules does not harden completely.
If the polymerizable monomer which is the content of the microcapsules includes abundant oxygen, various problems result such as a sufficiently strong polymer cannot be produced because the polymerization initiator is inactivated by the oxygen, the grown-polymer-radical reacts with the oxygen, and a low polymer is produced.